Treatment of solid substances at higher temperatures under action of gases



1953 H. WENDEBORN 3 TREATMENT OF SOLID SUBSTANCES AT HIGHER TEMPERATURES UNDER ACTION OF GASES Filed March 24, 1950 By g A e/1575 Patented Oct. 27, 1953 TREATMENT OF SOLID SUBSTANCES AT HIGHER TEMPERATURES UNDER AC- TION OF GASES Helmut Wendeborn, Seulberg, near Frankfurt am Main, Germany, assignor to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main,

Germany,

a corporation of Germany Application March 24, 1950, Serial No. 151,800 In Germany April 28, 1949 4 Claims. 1

This invention relates to certain improvements in the installations for the treatment of solid substances at higher temperatures under action of gases, such as the burning of cement, the calcining of limestone, the roasting of sulphurated ores, and has particular reference to a furnace for the manufacture of cement and similar substances.

In the operation of shaft furnaces for the burning of cement it is disadvantageous that a uniform charging of the fuel-containing raw cement powder is very difficult to attain in shaft furnaces of the conventional construction. Also the distribution of the blast over the cross section of the shaft furnace cannot be sufficiently controlled. The passage of air through the charge is not always uniform and as a rule takes place in the border zones, while the stock column in the center is only insufficiently traversed by air. As a result, the product is non-uniformly burnt and the cement produced from shaft furnace clinkers is not always uniform.

It is an object of the present invention to provide a furnace for the burning of cement and similar raw materials which permits a uniform charging of the burden and a distribution of the processing air in accordance with the requirements. With this and further objects in view, which will hereinafter appear, according to the present invention the furnace is dimensioned in a way which is fundamentally different from the conventional form, and on the other hand, the processing air is not blown into the charge from below, but it is sucked through the charge from the bottom to the top. More particularly, according to the invention the useful height of the furnace is less than its diameter or, in case of a rectangular furnace than its cross sectional diagonal and the furnace is provided with a device for the controlled sucking-through of the processing air or of other processing gases in the direction from the bottom to the top of the furnace.

It is known per se to suck air from the bottom to the top through the charge of shaft furnaces. It has been found, however, that this measure does not improve the imperfect distribution of the air in the shaft furnace, since the air during the long way through the shaft furnace has sufficient time and chance to take the path of minimum resistance. Therefore, it has been suggested already to operate with a low height of stock in the shaft furnace and on the other hand to blow the air into the furnace with the aid of a nozzle arrangement reaching to the middle of the stock,

2 in order to attain a better distribution of the air.

However, the proposals of this kind did not lead to a satisfactory result. The charging process remained imperfect and so also no uniform passage of air and no uniform burning process could be achieved.

The present invention, therefore, is based on the knowledge that a fundamental change of the conditions and so a uniformly burnt material can be attained only if the cross section of the furnace is increased and the processing air is fed into the charge or stock and through the same under action of a suction device. In a furnace whose useful height according to the present invention is smaller than its diameter or its cross sectional diagonal, the material can be easily charged in uniform layers and a low height of stock which is favourable for the burning process will automatically result. Moreover, no difficulties will be encountered in arranging adjustable air inlets within the stock and if desired, at the side of the furnace, in such a way that the entering air gets into the stock or charge uniformly distributed over the cross section of the furnace and traverses the same uniformly on the short path resulting owing to the low height of stock, under action of the suction from above.

According to a further important feature of the invention the grate is movable, whereby the material under treatment is continuously loosened in the lower layers, broken off and discharged through the interstices between the bars of the grate. The finished material discharged at the bottom may be replenished from the top in the measure as it is being discharged, by the addition of new raw material. Thus a continuous operation and so a high economy of the furnace will result, which is further improved by the fact that the costs for installing and maintaining the plant are relatively low as compared to the known evices for the burning of cement and the like.

The invention will be better understood by reference to the following detailed description in connection with the accompanying drawings, showing by way of example and purely schematically one embodiment of the invention and in which:

Fig. 1 is a vertical section of a furnace having the invention applied thereto, with a round cross section, and

Fig. 2 is a section on the line A-B in Fig. 1. Referring now to the drawing in greater detail it will be seen that the useful height of the furnace, denoted l, is smaller than the diameter, in accordance with the invention. Provided above 3 the furnace is a suction blower 2 with a chimney 3. The air is sucked off through a pipe 4 which terminates in the interior of the furnace and connects the same to the blower 2, through a dust separator 5, for instance, of the type known as Multiklon. A throttle valve 6 is arranged in the connecting pipe between the dust separator and the blower 2, for regulation of the suction air. The bottom of the furnace is formed by a perforated revolving grate 1 provided with upwardly directed ribs 1a for crushing or breaking the lower layers of the stock or charge. of the revolting grate is formed by a cone 8with air passages in its outer shell projecting into the interior of the furnace. A throttle organ, for

The center instance a throttle valve 8a which if desired may a be automatically controlled according to thefu-rnace temperature by means of a thermostat, serves for regulating the air entering into the cone. The revolving grate is movably supported in known manner on rollers 9, and driven by lateral rollers ID. In order to prevent the agglomerating charge from revolving with the grate, longitudinal ribs i I are provided in the shaft of the furnace, which ribs project beyond the furnace lining into the interior of the furnace. By way of alternative, the longitudinal ribs may be replaced by other installations suitable for this purpose.

The furnace is charged from the storage bunkers l2 under which is arranged a conveyer belt I3. feeding the ingredients of the charge to the mixing drumv [4. From the mixing drum M the, raw mixture is fed into the furnace through a further conveyer belt 15: and a plate feeder it.

Arranged. underneath the revolving grate I is a, discharge hopper l1 corresponding to the cross section of the furnace and conveying the processed charge to a crushing mill or-rolling crusher [8. The crushed material drops into a screen conveyer l9 and through this into tanks 26 and 2|, separated into finished material and return material.

By way of alternative the furnaceaccording to the; invention may have a, rectangular cross section, in which case the useful height has to be made smaller than the crosssectional. diagonal. In a furnace of this type the lower closure of the furnace is, formed by a grate which is adapted to bemoved to, and. fro in a longitudinal direction. The projecting ribs H: of the shell or wall of the furnace are unnecessary in this case.

The operation. of the furnace according to the invention is as follows: The constituents of the charge stored separately in. the bunkers l2, see Fig. l, in the form of raw powder, coal, and return material are fed to the furnace in the required proportions through a conveyer belt 13 and a mixing drum M. In the furnace the material charged is uniformly distributed over the whole cross-section ofthe furnace by means of the plate distributor It. The composition and preparation of the mixture are advantageously effected in the manner as usual in the operation of sinter apparatuses. Thus, for instance, the raw mixture consisting of raw cement powder and fuel is advantageously subjected to a crumbling operation in a mixing drum, with the addition of water, so as to facilitate the passage ofair through the charge.

Theair for combustion enters into the furnace under action of the suction device 2 producing a working depression of about to 80 centimeters water column or more, being uniformly distrib uted over the whole cross section of the revolving rate 1, and heated in the finish-burnt lower layers of the charge; thus preheated it gets into the burning zone: in whichthe-v material is clinkered or sintered depending on the amount of fuel added. The hot gases of combustion discharged from the burning zone then preheat the layers of the charge superposed thereto, evaporate the water from the crumbs or granules and finally pass out into the free air through the dust separator 5 and the suction device 2.

By operation of the throttle valves 6 and 8a it is possible to regulate the quantity and distribution. of the air and to adapt it to the temperature conditions of the furnace in the desired manner. Thusin case of a given amount of chargethe suction advantageously will be adjusted so that the temperature in the hood or bonnet of the furnace does not exceed, for instance, 200 C. The regulation may be effected automatically in dependence of a thermostat. It is also possible to throttle orv to increase in the desired manner the feed of air into the middle of the charge which is increased by the provision of the cone 8. Irregularities of the burningprocess, which should proceed in one plane, can easily be governed by the regulating devices and it is thus possible to keep the main combustion always within the region of the same zone.

The lower finish-burned layers are uniformly crushed or broken by the movable grate and' discharged through the interstices of the grate. The clinker is disintegrated in the rolling crusher :8 or in another suitable crushing mill, advantageously to grains of less than 30 millimeters, and then the fine material consisting substantially of insufiiciently burnt material, of a grain size up to 6 millimeters, is screened off and may be added again to the raw mixture, as return material. In the same way the dust accumulating in the dust separator 5' may continuously be fed back to the chargeof the furnace.

It willbe understood that the furnace according to the present invention is not only suitable for the burning of cement, but it islikewise applicable for the carrying out of other burning processes, e. g. for the burningof lime, the roast?- ing or. calcining of iron ores or for other. processes in which the heat treatment of, solid substances under action of. air or gasesis required.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made. without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modification in. the. appended claims.

Having thus. describedv my invention, I claim as new and desire to secure by Letter Patent:

1. A furnace. for the treatment of solid substances at. high temperatures under action of gases, comprising a reaction chamber, a gas permeable rotatable grate extending substantially over the entire bottom of said reaction chamber, adapted toreceive thereon a charge of'the substance to be processed in the furnace, mean disposed above said grate to suck gas through said grate and through the charge upon said grate, said. suction means being the sole device within. said furnace for activating the movement of the gas through the furnace, said movable grate acting simultaneously as a discharge device for the processed charge, means for feeding said charge into the reaction chamher, and the useful height of said reaction chamber being smaller than its largest horizontal cross-sectional dimension.

2. A furnace for the treatment of solid substances at high temperatures under action of gases as in claim 1, wherein the center position of said grate is formed as a cone projecting into the reaction chamber, and having vent holes, and comprising in addition a throttle member for regulating the quantity of gas passing through said vent holes.

3. A furnace for the treatment of solid substances at high temperatures under action of gases as in claim 1, comprising in addition upright ribs projecting from the walls of the furnace into the interior of the reaction chamber and extending from the bottom of the reaction chamber to at least the useful height thereof, so as to prevent the simultaneous motion of the charge and the movable grate.

4. A furnace for the treatment of solid substances at high temperatures under action of gases as in claim 1, wherein the said suction control means comprise a throttle member inserted between the suction means and ,the reaction chamber, and means for controlling said throttle member in dependence of the term perature of the gases in the reaction chamber.

HELMUT WENDE'BO'RN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 399,795 Taylor Mar. 19, 1889 1,533,931 Lummis Apr. 14, 1925 1,923,084 Gillette Aug. 22, 1933 1,924,820 Van Ackeren Aug. 29, 1933 2,070,235 Mullen Feb. 9, 1937 2,498,710 Boetheli Feb. 28, 1950 2,520,384 Davis Aug. 29, 1950 FOREIGN PATENTS Number Country Date 27,821 Netherlands Sept. 15, 1932 

